Diabetics lack sensation in the plantar or bottom surface of the foot and, typically, have a reduced amount of fatty tissue at that location. Accordingly, they are particularly susceptible to skin irritation and breakdown occasioned by frictional contact between the plantar surface of the foot and the insole of the shoe. This frictional contact results from torsion between the foot and pelvis, which causes transverse foot rotation during the normal walking motion. Such rotation results in shear stresses between the plantar surface of the foot and the surface with which it comes in contact (the insole of the shoe or the floor). Since diabetics lack sensation in the foot and are more susceptible to irritation, it is not uncommon for them to develop plantar ulceration.
It is therefore an object of the present invention to provide an orthotic shoe which will substantially reduce or eliminate abrasive contact between the plantar surface of the foot and the insole of a shoe occasioned by transverse rotation of the foot during normal walking. It is specifically contemplated that the invention would provide a sole construction in which the transverse rotation of the foot would be absorbed by the shoe sole.
It is another object of the invention to provide an orthotic shoe and sole construction to substantially reduce or eliminate abrasive contact between the plantar surface of the foot and a shoe insole, which are reliable and convenient in use, yet relatively simple and inexpensive in construction.
In accordance with the present invention, a shoe sole is constructed with a relatively rigid top layer or insole and a relatively rigid bottom layer or outsole which are mounted for relative rotation about an axis perpendicular to and extending through the center of the sole. Between the insole and outsole, there is provided a relatively yieldable elastomer layer, which permits relative rotation between the insole and the outsole upon rotation of the foot during walking, but resiliently restores the insole and outsole to an aligned position when the torsional force of the foot is removed.